BENTHIC MACROINVERTEBRATE INDEX

Brief Summery:

The term "benthic" means bottom-dwelling. Benthic invertebrates are animals without backbones that live in, crawl upon, or attach themselves to the bottom (substrate). The term "macroinvertebrates" refers to those invertebrates seen with the unaided eye. Most benthic macroinvertebrates in flowing water are aquatic insects or the aquatic stages of insects. Other benthic macroinvertebrates include other arthropods, worms, and clams.

Benthic macroinvertebrates often go unnoticed because of their size and habitat, but they are an extremely important part of river ecosystems. Collecting benthic macroinvertebrates can provide a greater understanding of a river's condition. Benthic organisms have several characteristics that make them useful indicators of water quality. For example, they are sensitive to physical and chemical changes in their habitat. Also, they live in the water for the entire aquatic stage of their life cycle and so reflect conditions in the water throughout that period of time. Third, benthic organisms cannot easily by swimming away, as some fish can. Finally benthic macroinvertebrates are easily collected in many streams and rivers.

We will classify benthic macroinvertebrates into three groups based on their sensitivity to pollution. The number of taxa in each of these groups will be tallied and assigned a score. The scores are then summed to yield a score which can be used as an estimate of the quality of the watercourse for life.

METRICS WITHIN THE BENTHIC MACROINVERTEBRATES:

1. GROUP ONE TAXA: Pollution-Sensitive Organisms
These organisms are highly sensitive to pollution. Each group of these animals which is found is given a score of 3 toward the overall index value.
2. GROUP TWO TAXA: Pollution-Intermediate Organisms
These organisms are somewhat less sensitive to pollution, but they cannot live in very polluted water. Each group of these animals which is found is given a score of 2 toward the overall index value.
3. GROUP THREE TAXA: Pollution-Tolerant Organisms
These organisms are rather insensitive to pollution. While they require basic resources for life, they can be found in fairly polluted water. Each group of these animals which is found is given a score of 1 toward the overall index value.
4. GROUP FOUR TAXA: Other Invertebrates
These organisms are not included in the Ohio Department of Natural Resources' Benthic Macroinvertebrate Index. However, you are likely to see them in most streams in Ohio.

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